Enantioselective hydrogenation of activated ketones in the presence of Pt–cinchona catalysts. Is the proton transfer concept valid?

• The Orito’s reaction was investigated in case of four different activated ketones.
• The effect of achiral amines and nitrogen containing aromatics was studied.
• According to proton transfer concept, the chiral and racem cycles would compete.
• Achiral amine additives did not decrease the enantiomeric excess in either case.
• Direct proton-transfer from Pt to the substrate via cinchonidine can be questioned.

Experimental evidences related to the proton transfer in the catalytic system Pt–cinchona alkaloids for enantioselective hydrogenation of activated ketones were collected and analyzed. Both new and earlier results indicate that in aprotic media direct transfer of proton from platinum to the substrate with the involvement of quinuclidine nitrogen as a general rule can be questioned.